A semiconductor light emitting element used for a light emitting diode, a laser diode, or the like can be obtained by forming a light emitting layer, which emits light, on a sapphire or GaN substrate. In the light emitting layer, an active layer for emitting light is interposed between a p-type semiconductor and an n-type semiconductor.
The active layer emits light using a forward current at a pn junction. Therefore, when the active layer is formed flat, a current needs to be uniformly supplied to the flat active layer to improve luminous efficiency.
In order to uniformly supply a current to the flat active layer, a p-side electrode and an n-side electrode may be respectively attached to the p-type and n-type semiconductors, between which the active layer is interposed. However, when electrodes are arranged, which completely cover the semiconductors on and under the active layer, light cannot be obtained from the active layer.
Therefore, when two electrodes of p-side and n-side are provided on one surface of a substrate, special care needs to be taken to determine shapes of the electrodes, or a transparent electrode made of, e.g., ITO is used for one of the electrodes.
As an example, Patent Document 1 shows a semiconductor light emitting element, in which an active layer having a relatively large area is formed on a substrate made of a material such as sapphire, which has a low electrical conductivity. Electrodes are arranged in a comb-like shape to uniformly supply a current to the active layer, and a p-side electrode in any position is spaced apart from an n-side electrode by a predetermined distance or less.
On the other hand, when a conductive substrate is used as the substrate, on which a light emitting layer is formed, since a current passes through the substrate, the current can be relatively uniformly supplied from a p-side to an n-side, even if two electrodes of p-side and n-side are provided on one surface of the substrate. However, in this case, since the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are stacked sequentially, an electrode supplying a current to one of the semiconductor layers needs to be formed after removing the active layer. This reduces the area of emitting light. Thus, an electrode for one of the semiconductor layers is formed with a large area, and an electrode for the other semiconductor layer is formed with a small area. Typically, a p-side electrode is formed with a large area, and an n-side electrode is formed with a small area.
As an example of this semiconductor light emitting element, Patent Document 2 shows a semiconductor light emitting element, in which a p-side electrode and an n-side electrode are formed on one surface of a conductive GaN substrate. In this semiconductor light emitting element, an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are sequentially formed on a substrate. The p-side electrode is formed on the p-type semiconductor layer. The n-side electrode is formed on the n-type semiconductor layer after removing the p-type semiconductor layer and the active layer. The n-side electrode is formed at only one corner of the substrate.
PATENT DOCUMENT 1: Japanese Patent Publication No. 2004-47988
PATENT DOCUMENT 2: Japanese Patent Publication No. 2007-266427